Bill Carey

U.S. government and industry testers plan to begin data-gathering flights later this year using a system that will address perhaps the biggest technological hurdle to widespread use of unmanned aircraft systems (UAS)–the ability of a remotely piloted vehicle to “detect and avoid” (DAA) other aircraft. At the same time, a special committee convened by standards organization RTCA is working toward delivering DAA equipment standards by July 2016.


General Atomics, Honeywell, BAE Systems, the U.S. Federal Aviation Administration (FAA) and NASA will evaluate a DAA system with “self-separation” functionality using NASA’s Ikhana air vehicle–a General Atomics’ MQ-9 Predator B–during flight tests that are scheduled to begin in November at NASA’s Armstrong Flight Research Center, part of Edwards Air Force Base in California. The DAA system architecture combines automatic dependent surveillance-broadcast (ADS-B) position reporting and TCAS collision avoidance, which are both transponder-based “cooperative” technologies requiring other aircraft to be so equipped, and the General Atomics “due-regard” radar, an active electronically scanned array (AESA) X-band radar that can detect “non-cooperative” aircraft, that is, those without transponders.


The testers also plan to introduce an advanced airborne collision avoidance system-X (ACAS X) algorithm the FAA is studying for unmanned aircraft, known as ACAS Xu, developed by MIT Lincoln Laboratory.


Self-separation is the ability of an aircraft to remain “well clear,” or safely separated from other aircraft. Due regard, a term that originated with the International Civil Aviation Organization (ICAO), refers to a requirement that military and state-owned aircraft be flown with “due regard for the safety of navigation of civil aircraft” when operating over international waters.


Last November, General Atomics conducted the first flight of a DAA system on a company-owned Predator B flown from its Gray Butte flight operations facility in Palmdale, California. The system combined a prototype due-regard radar, BAE’s AD/DPX-7 identification friend or foe transponder with ADS-B in reception and Honeywell TPA-100 TCAS processor, working in unison to detect and track cooperative and non-cooperative aircraft. Honeywell’s sensor fusion algorithm combined data from the multiple sensors into a single track for display in the ground control station, where General Atomics’ conflict prediction and display system aids the pilot in maneuvering the aircraft to stay well clear of traffic.


In an interview with AIN, General Atomics executives said self-separation is managed by the pilot on the ground, based on the fused sensor information sent to the ground control station. Track data for collision avoidance, a function of last resort, will be sent both to the ground and directly to the aircraft’s flight computer. The system’s TCAS function and autopilot are coupled. The pilot will have about three or four seconds to respond to a resolution advisory, or recommended evasive action; otherwise the autopilot will perform the maneuver.


As efforts to introduce unmanned aircraft into the U.S. national airspace system gather steam, RTCA Special Committee 228, an industry and government group established in May 2013, is developing minimum operational performance standards (Mops) for both DAA capability and the communications and control (C2) datalink that UASs will need to safely fly in nonsegregated airspace. Mops describe technical characteristics and test procedures for avionics systems andcomponents, which the FAA may then incorporate into technical standard orders that manufacturers follow to design and build equipment.


SC-228’s initial focus is to develop DAA standards for larger unmanned aircraft equipped to operate in Class-A airspace above 18,000 feet MSL under IFR flight rules, transitioning through lower airspace levels to get there. It expects to produce preliminary Mops for both DAA and C2 systems by next July, with final standards following a year later.


At the Unmanned Systems 2014 conference in Orlando, Florida, in May, Satish Krishnan, General Atomics technical director of special projects, said the company’s internally funded due-regard radar development, started in 2011 with a “breadboard” AESA radar on a manned aircraft, had completed 28 manned and two unmanned flight tests, with 80 hours of flight time. General Atomics plans to make available preproduction engineering development model radars to customers in the first quarter of 2015. The full DAA suite will be designed to specifications RTCA released in 2016. “We have a good idea of where the industry is in terms of development, and we are the industry leader,” Krishnan told AIN.


Other efforts are progressing in the U.S. to develop DAA systems for unmanned aircraft, a capability earlier and alternately known as “sense and avoid.” The U.S. Air Force started a formal acquisition program in October 2012 for what at the time was a Global Hawk-specific technology. In January 2013, the service adopted a new strategy to develop a common airborne sense-and-avoid system (C-ABSAA). Last September, it issued to industry a request for information seeking potential sources to develop a C-ABSAA system “for large remotely piloted aircraft systems including the Predator and Global Hawk.” General Atomics, for one, confirmed that it responded to the solicitation.


The Mitre Corporation joined with NASA Langley Research Center, the University of North Dakota (UND) and Draper Laboratory to test a DAA system using ADS-B as the sensor in 2011. The aim of the Limited Deployment-Cooperative Airspace Project (LD-CAP) was to test a “cooperative autonomous sense-and-avoid” system that would work even if a C2 link to the aircraft was interrupted. Tests involved flying a NASA-Langley Cirrus SR22 single-engine airplane as a “surrogate” UAS, with a safety pilot aboard, to evaluate software maneuver algorithms based on ADS-B detection of nearby aircraft. The project ran some 400 encounters in flight against UND and NASA-flown “intruder” airplanes.


At the Unmanned Systems conference, Al Palmer, director of the UAS Center of Excellence at UND, said the LD-CAP project will be extended, and will likely incorporate Northrop Grumman’s SandShark UAS. The university and Northrop Grumman also signed a cooperative agreement to offer pilot training using the SandShark.

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